QUANTITATIVE INHIBITION OF PROGESTERONE BY ESTROGENS IN DEVELOPMENT OF DECIDUOMATA1

Abstract

Six estrogens were compared as to their ability to inhibit the decidual growth in rats induced by a standard dose of progesterone. The rats were castrated on the 5th day of pseudopregnancy, 1 horn of the uterus traumatized by scratching the endometrium on the antimesometrial surface throughout its entire length, and each animal was given 1.5 mg. progesterone daily for 3 days and killed 72 hrs. after the 1st injn. Deciduomata produced by this method were approx. of the same diameter as those found in normal animals on the 4th day following uterine traumatization on the 5th day of pseudo-pregnancy. Each estrogen was tested to determine (1) the minimal daily dose that could be given concurrently with 1.5 mg. progesterone without modifying the decidual raction, (2) the amts. that would reduce the reaction 25%, 50% 75%, and (3) the minimal dose that would give total inhibition. 17-beta Estradiol was by far the most active inhibitor. The other estrogens listed in order of their effectiveness were estradiol benzoate, diethyl-stilbestrol, estrone, estriol, and equilenin, the latter 2 being 200-300 and 300-400 times less active than estradiol.